I think at butt connector would have the wires sliding in from different sides, Dan. It looked me like that was the case in your picture. In that case the wires would overlap. You want the heat shrink to "draw down" on only one wire (that's why they have to come from both sides, so his like a waterproof clamp around the wire insulation.)

The reason that I like the longer "shaft" is that it really keeps any copper from being exposed to the LITTLE air in the seal.

If you can heat strink it nicely to seal it, and you can get to it again, and you will stll have enough extra wire to do it a couple of more times in the future of the life of the boat....Then go for it. But make sure the heat shrink does its job without "burning" the conector and damaging it.